Commit eb04c282 authored by Jan Kara's avatar Jan Kara Committed by Al Viro
Browse files

fs: Add freezing handling to mnt_want_write() / mnt_drop_write() 

Most of places where we want freeze protection coincides with the places where
we also have remount-ro protection. So make mnt_want_write() and
mnt_drop_write() (and their _file alternative) prevent freezing as well.
For the few cases that are really interested only in remount-ro protection
provide new function variants.

BugLink: https://bugs.launchpad.net/bugs/897421


Tested-by: default avatarKamal Mostafa <kamal@canonical.com>
Tested-by: default avatarPeter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: default avatarDann Frazier <dann.frazier@canonical.com>
Tested-by: default avatarMassimo Morana <massimo.morana@canonical.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 5accdf82

fs/file_table.c

+1 −1
Original line number Diff line number Diff line
@@ -217,7 +217,7 @@ static void drop_file_write_access(struct file *file) 
		return;

	if (file_check_writeable(file) != 0)

		return;

	mnt_drop_write(mnt);

	__mnt_drop_write(mnt);

	file_release_write(file);

}

fs/inode.c

+2 −2
Original line number Diff line number Diff line
@@ -1660,11 +1660,11 @@ int file_update_time(struct file *file) 
		return 0;



	/* Finally allowed to write? Takes lock. */

	if (mnt_want_write_file(file))

	if (__mnt_want_write_file(file))

		return 0;



	ret = update_time(inode, &now, sync_it);

	mnt_drop_write_file(file);

	__mnt_drop_write_file(file);



	return ret;

}

fs/internal.h

+4 −0
Original line number Diff line number Diff line
@@ -61,6 +61,10 @@ extern void __init mnt_init(void); 


extern struct lglock vfsmount_lock;



extern int __mnt_want_write(struct vfsmount *);

extern int __mnt_want_write_file(struct file *);

extern void __mnt_drop_write(struct vfsmount *);

extern void __mnt_drop_write_file(struct file *);



/*

 * fs_struct.c

fs/namespace.c

+77 −20
Original line number Diff line number Diff line
@@ -283,24 +283,22 @@ static int mnt_is_readonly(struct vfsmount *mnt) 
}



/*

 * Most r/o checks on a fs are for operations that take

 * discrete amounts of time, like a write() or unlink().

 * We must keep track of when those operations start

 * (for permission checks) and when they end, so that

 * we can determine when writes are able to occur to

 * a filesystem.

 * Most r/o & frozen checks on a fs are for operations that take discrete

 * amounts of time, like a write() or unlink().  We must keep track of when

 * those operations start (for permission checks) and when they end, so that we

 * can determine when writes are able to occur to a filesystem.

 */

/**

 * mnt_want_write - get write access to a mount

 * __mnt_want_write - get write access to a mount without freeze protection

 * @m: the mount on which to take a write

 *

 * This tells the low-level filesystem that a write is

 * about to be performed to it, and makes sure that

 * writes are allowed before returning success.  When

 * the write operation is finished, mnt_drop_write()

 * must be called.  This is effectively a refcount.

 * This tells the low-level filesystem that a write is about to be performed to

 * it, and makes sure that writes are allowed (mnt it read-write) before

 * returning success. This operation does not protect against filesystem being

 * frozen. When the write operation is finished, __mnt_drop_write() must be

 * called. This is effectively a refcount.

 */

int mnt_want_write(struct vfsmount *m)

int __mnt_want_write(struct vfsmount *m)

{

	struct mount *mnt = real_mount(m);

	int ret = 0;
@@ -326,6 +324,27 @@ int mnt_want_write(struct vfsmount *m) 
		ret = -EROFS;

	}

	preempt_enable();



	return ret;

}



/**

 * mnt_want_write - get write access to a mount

 * @m: the mount on which to take a write

 *

 * This tells the low-level filesystem that a write is about to be performed to

 * it, and makes sure that writes are allowed (mount is read-write, filesystem

 * is not frozen) before returning success.  When the write operation is

 * finished, mnt_drop_write() must be called.  This is effectively a refcount.

 */

int mnt_want_write(struct vfsmount *m)

{

	int ret;



	sb_start_write(m->mnt_sb);

	ret = __mnt_want_write(m);

	if (ret)

		sb_end_write(m->mnt_sb);

	return ret;

}

EXPORT_SYMBOL_GPL(mnt_want_write);
@@ -355,38 +374,76 @@ int mnt_clone_write(struct vfsmount *mnt) 
EXPORT_SYMBOL_GPL(mnt_clone_write);



/**

 * mnt_want_write_file - get write access to a file's mount

 * __mnt_want_write_file - get write access to a file's mount

 * @file: the file who's mount on which to take a write

 *

 * This is like mnt_want_write, but it takes a file and can

 * This is like __mnt_want_write, but it takes a file and can

 * do some optimisations if the file is open for write already

 */

int mnt_want_write_file(struct file *file)

int __mnt_want_write_file(struct file *file)

{

	struct inode *inode = file->f_dentry->d_inode;



	if (!(file->f_mode & FMODE_WRITE) || special_file(inode->i_mode))

		return mnt_want_write(file->f_path.mnt);

		return __mnt_want_write(file->f_path.mnt);

	else

		return mnt_clone_write(file->f_path.mnt);

}



/**

 * mnt_want_write_file - get write access to a file's mount

 * @file: the file who's mount on which to take a write

 *

 * This is like mnt_want_write, but it takes a file and can

 * do some optimisations if the file is open for write already

 */

int mnt_want_write_file(struct file *file)

{

	int ret;



	sb_start_write(file->f_path.mnt->mnt_sb);

	ret = __mnt_want_write_file(file);

	if (ret)

		sb_end_write(file->f_path.mnt->mnt_sb);

	return ret;

}

EXPORT_SYMBOL_GPL(mnt_want_write_file);



/**

 * mnt_drop_write - give up write access to a mount

 * __mnt_drop_write - give up write access to a mount

 * @mnt: the mount on which to give up write access

 *

 * Tells the low-level filesystem that we are done

 * performing writes to it.  Must be matched with

 * mnt_want_write() call above.

 * __mnt_want_write() call above.

 */

void mnt_drop_write(struct vfsmount *mnt)

void __mnt_drop_write(struct vfsmount *mnt)

{

	preempt_disable();

	mnt_dec_writers(real_mount(mnt));

	preempt_enable();

}



/**

 * mnt_drop_write - give up write access to a mount

 * @mnt: the mount on which to give up write access

 *

 * Tells the low-level filesystem that we are done performing writes to it and

 * also allows filesystem to be frozen again.  Must be matched with

 * mnt_want_write() call above.

 */

void mnt_drop_write(struct vfsmount *mnt)

{

	__mnt_drop_write(mnt);

	sb_end_write(mnt->mnt_sb);

}

EXPORT_SYMBOL_GPL(mnt_drop_write);



void __mnt_drop_write_file(struct file *file)

{

	__mnt_drop_write(file->f_path.mnt);

}



void mnt_drop_write_file(struct file *file)

{

	mnt_drop_write(file->f_path.mnt);

fs/open.c

+1 −1
Original line number Diff line number Diff line
@@ -620,7 +620,7 @@ static inline int __get_file_write_access(struct inode *inode, 
		/*

		 * Balanced in __fput()

		 */

		error = mnt_want_write(mnt);

		error = __mnt_want_write(mnt);

		if (error)

			put_write_access(inode);

	}

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